Extended surface heat exchanger



E. s. LEA 2,278,086

EXTENDED SURFACE HEAT EXCHANGE March 31; 1942;.

Filed Jan. 2'," 1940 INVENTOR i mamdf a jay zyw P ATTORNEYS Patented Mar. 31, 1942 EXTENDED SURFACE HEAT EXCHANGER Edward S. Lea, Morrisville, Pa., assignor to Buensod-Stacey Air Conditioning, Incorporated, New York, N. Y., a corporation of Delaware Application January 2, 1940, Serial No. 312,007

5 Claims.

This invention relates to heat interchange apparatus and more particularly to improvements in heat exchange units which may be used as parts of a heating system for a building or for cooling air passing over its surfaces.

One of the objects of the invention is to pro- Vide a heat exchange unit of the light weight extended surface type, having its transfer tubes so arranged and supported that they may freely expand when heated, or contract under other conditions, independently of one another, without generating forces which might destroy those tubes or their joints with the supply and discharge headers of the unit.

It is a further object to provide a heat exchanger of the foregoing character having U- shaped tubes with their legs all lying in a common plane to form what is known as a single row unit, as well as to provide one wherein the legs of its tubes are disposed in different planes in more or less conventional fashion to form a double row device.

These and other objects of the invention, as well as various features thereof, will be more fully understood from a consideration of the following description in the light of accompanying drawing in which:

Fig. 1 is a plan View of aheat exchange unit wherein the tubes are arranged in a single row in accordance with one form of the invention; and

Fig. 2 is a sectional View taken on the line 2-2 of Fig. 1.

The heat exchanger of Figs. 1 and 2 employs a series of U-shaped tubes l carrying a large number of closely spaced fins II and providing passages for the flow of a warmed or cooled medium from the supply header l2 to the discharge header 13 in heat exchanging relation with a stream of air passing over their outer surfaces. These tubes are usually made of copper although aluminum or other metals are sometimes used, and they may readily be formed by bending a single section of tubing upon itself, or, as is here shown, by interconnecting the ends of separate legs Illa and [0b by return bends [4.

It is particularly of note that the tubes are arranged in a common plane to provide what is known as a one-row device. In order to accomplish this, and yet permit of their attachment to the superposed supply and discharge headers, the ends of the tubes are disposed at angles to the horizontal, and the nipples of the headers are arranged at complementary angles. Thus, the end portions l5 of the supply legs lfla are bent upwardly .to join the downwardly extending nipples N5 of the supply header [2, while the end portions I! of the discharge legs lUb are bent downwardly for connection with the upwardly directed nipples N3 of the discharge header l3. It has been found that with the horizontal provides a satisfactory angle. It does not require too long an end portion nor is it so sharp as to result in the cracking of the tube. The angle, however, may be somewhat more acute, or on the other hand, somewhat less so,

as circumstances warrant.

The headers are of conventional form except in so far as the mentioned angular disposition of their nipples is concerned, each comprising a hollow body portion having a row of the nipples l6, l8 formed thereon and a coupling portion I9, 20 extending rearwardly for connection to a supply or discharge line. The nipples here illustrated are adapted snugly to receive the ends of the tubes which may then be aflixed therein by the application of solder. Other forms of nipples are well-known, however, and may be employed if desired. It will also be noted (Fig. 1) that the supply coupling I 9 is formed at the mid-point of the supply header [2 while the discharge coupling 20 is located at an end of its header l3. This arrangement is preferred, but an equal or greater ofisetting of the couplings may be obtained by forming them at the opposite ends of the respective headers. It will be further noted that the supply coupling I9 carries a radial fiange 2| by which it and the header l 2 may be rigidly attached to a supporting structure; and that the discharge header l3 has no comparable element.

After assembly of the tubes and their headers these parts are mounted in a casing 22 which serves to facilitate the installation of the unit as well as to confin air to contact only with the tubes and their fins. In mounting these heat exchange elements it will be noted that they are rigidly attached to the casing at but one point. Thus the supply header l2 has its coupling l9 extending through an opening 23 in one end of the wall 24 of the casing and its flange 2| bolted thereto as indicated at 25. The discharge header, however, is not so attached. Its coupling 20 merely extends through the opening 26 so that it is supported by the end wall 24, but is entirely free to move in a direction lengthwise of the casing. Similarly, th return bends M are disposed in slot-like openings 26:: of the opposite end wall 21 So that they too are merely supported, but are not otherwise confined.

With this arrangement, the U-shaped tubes may expand or contract freely. Thus the lengthening or shortening of them is accommodated by the mere sliding of the return bends in their non-rigid support. Uniform expansion and contraction meets no opposition and accordingly results in the imposition of no force of a destructive nature on the tubes or their joints with the headers. The arrangement has the further advantage of avoiding any twisting stresses on the headers when one set of legs of the tubes expand more than the other ones. When, for example, steam is admitted to the unit and all of it is condensed in the supply legs Illa, then those supply legs will be heated to a much higher temperature than the discharge ones lllb which contain only relatively cool condensate. The supply legs accordingl expand to a somewhat greater extent than do the discharge ones. In this expansion the return bends are moved in their non-rigid support just as previously mentioned and the difference in length between the supply and discharge legs is accommodated by a movement of the discharge header [3 away from the end wall 24 of the casing. Free movement of the discharge header accordingly avoids any possibility of a flexing or twisting of the separate legs of the tubes in accommodating their differential expansion.

In order to protect the tube ends and to prevent by-passing of air around them, a channel-shaped baffle 28 is afiixed to the end wall 21 in such position as to cover the return bends l4. Similarly, baffles 29 are mounted on the other end wall in such positions as to extend over the headers l2 and I3 and the un-finned end portions of the tubes l0.

Since certain changes may be made in the embodiment of the invention without in an way departing from the teachings thereof, it is intended that the foregoing shall be construed in a descriptive rather than in a limiting sense.

What I claim is:

1. A heat exchange unit including a plurality of heat transfer tubes, each comprising a pair of I substantiall straight leg portions and a return bend portion, and supply and discharge headers arranged in substantially superposed relation, said tubes having their return bend portions and substantially all of their leg portions arranged in a single row, which is horizontally disposed when said headers are horizontally disposed, each of said tubes having one leg portion connected to said supply header and the other to said discharge header with one of said legs having a short end portion disposed at an angle to the remaining portion to facilitate its connection to the appropriate one of said headers.

2. A heat exchange unit, according to claim 1, further characterized in that said supply header is disposed above said discharge header, and in that the last mentioned leg of each tube has its end portion bent downwardly to facilitate its connection to the discharge header.

3. A heat exchange unit, according to claim 1, further characterized in that said supply header is disposed above said discharge header, and in that each tube has a short end portion of one of its legs bent upwardly for connection to said supply header and a short end portion of the other of its legs bent downwardly for connection to said discharge header.

4. A heat exchange unit including a plurality of heat transfer tubes each comprising a pair of substantially straight and parallel leg portions and a return bend portion, fins on said tubes for increasing their outer heat transfer surfaces, and supply and discharge headers disposed in substantially superposed relation with the supply header at the higher elevation, said tubes having their leg portions disposed in a single horizontal row, and each of said tubes having a short end portion of on of its legs bent upwardly and connected to said supply header and a short end portion of the other of its legs bent downwardly and connected to said discharge header.

5. A heat exchanger comprising a casing, supply and discharge headers disposed in said casing in substantially superposed relation, one of said headers being rigidly connected to said casing and the other being supported by the casing but being free to move with respect thereto, a plurality of U-shaped heat transfer tubes having their legs and return bends lying in a common plane, and each of said tubes having a relatively short portion adjacent the open end of one of its legs bent in a direction away from the common plane of the tubes and connected to said supply header, and a similar portion adjacent the open end of its other leg bent in the opposite direction and connected to said discharge header.

EDWARD S. LEA. 

